You could use dove pans to make some dishes appear in front of customers? a lot of the stuff you could do will depend on what level of skill your staff would have.
Christopher's suggestion is excellent, but would be predicated by your staff already having some skill in cups and balls or cd manipulation, or having the time, inclination, and opportunity to develop those effects.
Depending on your preferences, I would probably go for gimmicks rather than sleights, as I know the restaurant industry can have a high staff turnover.